This project's goal is to understand the role of cyclic AMP in the in vivo modulation of dopaminergic neurotransmission and consequent behavior. The neuron subtypes which will be studied are those expressing the dopamine receptOr subtypes D1, D2 and D5. Traditional pharmacological approaches to studying the regulation and function of specific dopaminergic neuron subtypes have been limited by the lack of complete specificity of dopamine receptor agonists and antagonists. An approach is proposed to directly investigate the regulation and function of these dopaminergic neuron subtypes by genetic perturbation of their regulatory second messengers in the transgenic mouse and rat. In this transgenic pharmacological approach, a cholera toxin transgene that elevates the intracellular levels of a major stimulatory intracellular second messenger, cyclic AMP (cAMP), will be fused to the transcriptional promoters of the D1, D2 and D5 dopamine receptor genes. Each of these fusion transgenes will be microinjected into mouse embryos to produce transgenic mutants in which functional alterations are induced precisely in each of these genetically- specified dopaminoceptive neuron subtypes. The cAMP-induced alterations in molecular and cellular physiology and neurotransmission in these mice will be examined, as well as their consequent effects on mouse neurological function and behavior, in order to address the following specific aims: 1. Determine if cAMP enhances neurotransmitter output from D1 neurons in vivo and causes psychomotor stimulation. 2. Determine if striatal D1 and D2 neurons are functionally distinct or identical neuron subtypes, and if other D1 and D2 neurons have functionally distinct roles in vivo. 3. Determine if D1 and D5 neurons have functionally distinct roles in vivo. Later, these transgenes will be delivered somatically in adenoviral vectors into particular regions of the brain, in order to query the role of cAMP in regulating the function of regionally-defined subpopulations of D1, D2 and D5 neurons. These data may help resolve unanswered questions about the specific functions of these regionally and biochemically-distinct classes of neurons, and in doing so, may help elucidate what roles the related human dopaminergic neuron subtypes play in several psychomotor disorders thought to involve the dopaminergic system. Moreover, this transgenic approach may contribute to the development of gene therapies for these disorders.